Re: A Tragedy of the Ninja World: Uchiha Obito
We really don't know much about Obito's true personality as a child. Given that Kishi has been drawing parallels between Naruto and Obito, it's entirely possible that he was ignored and neglected which, like Naruto, fed his rivalry with Kakashi who 'had everything'.
If that's the case, we simply need to ask ourselves what is it that kept Naruto from becoming a psychopath. The answer to that is obvious; He had people who acknowledged him and believed in his dreams.
And given what we've seen of Obito during his flashbacks, Obito honestly lacked that. He was constantly overlooked for Kakashi by everyone, even Rin. He made Chuunin, and what does Rin do? She doesn't celebrate or congratulate him, she invites him to a party to celebrate Kakashi's promotion, presumably without even telling him her intentions.
That's pretty low.
So Obito probably had a lot of hate. And let's think about what happened after Kannabi Bridge; Despite the fact that Obito sacrificed himself to save Rin and Kakashi and gave them the tools to complete their mission, Obito was probably remembered as nothing more than another casualty of war while Kakashi became 'the Hero'.
That'd piss anyone off.
So whoever retrieved Obito probably had a lot of hatred to work with. The personality shift really isn't that unlikely all things considered.